The exploitation of oil and gas wells constructions of hoses capable of operation under the conditions of high internal pressures and axial tensions. However, the existing hoses which provide for operation under the above conditions fail to offer adequate flexibility, which greatly complicates their use and transportation. On the other hand the conventional hoses which offer an adequate flexibility are incapable of operation under high axial tensions; this restricts the use of such hoses, for example rendering them completely unfit for lowering into a well or mine.
The problem of providing a flexible hose capable of operation under high internal pressures and axial tensions arose relatively long ago, but still remains to be adequately solved.
There is known in the art a hose disclosed in U.S. Pat. No. 3,715,454. The hose comprises an internal supporting portion in the form of spaced tubular members interconnected by convolutions which are integral with the tubular members and extend radially outwardly from the latter. The convolutions have aligned recesses which define at least one groove extending the full length of the hose, each groove accommodating a reinforcing thread secured to the hose over the entire length thereof.
The hose of the above-described construction may be, depending on the amount of the reinforcing threads, employed for operation either under the action of only an internal pressure or under a simultaneous action of both an internal pressure and an axial tension. In the latter case, an additional amount of the threads is provided to counterbalance the external axial tensile forces. However, increasing the amount of the threads considerably lowers the flexibility of the hose. Thus, the above-described hose reinforced in the axial direction will be capable of operation under a simultaneous action of a high internal pressure and high axial tensile forces, offering low volume, axial, and radial deformations, and a fair durability, but at the same time will have a high specific weight, will be difficult to manufacture and costly.
When adequately reinforced in the axial direction, the hose will have but a very low flexibility. Moreover, it will be incapable for operation in a bent state, since in this case the equality of loading of the reinforcing threads will be upset and thereby the carrying capacity of the construction as a whole will be lowered. The above disadvantages considerably restrict the scope of application of this known.
Another hose construction has been proposed in the French Pat. No. 2,142,764. This hose comprises an inner supporting tube of an elastic material and an outer protective cover, between which reinforcing plies are arranged. Each of the reinforcing plies has the form of a helically wrapped metallic braid, the wrapping angle with respect to the geometrical axis of the hose varying in accordance with a certain relationship from the innermost reinforcing ply to the outermost one within the range of 80.degree. to 6.degree..
The above-described hose features an adequate flexibility and is capable of withstanding the internal pressure. However, due to the high axial and volume deformations arising in operation, especially with a pulsating internal pressure, the threads of the reinforcing ply braids rub through due to their displacements with respect to one another, which greately impairs the durability of the hose. In addition, a hose of such a construction is incapable of operation under an axial tension.
There is also known in the art a hose disclosed in British Pat. No. 1,334,025. The hose comprises an inner supporting tube of an elastic material and an outer protective cover, between which reinforcing plies are arranged. Each of the reinforcing plies is a multiplicity or set of helically wrapped parallel threads, the angle of wrapping of the threads with respect to the geometrical axis of the hose varying in accordance with a certain relationship from the innermost reinforcing ply to the outermost one within the range of 80.degree. to 6.degree., and each of the reinforcing plies being disposed between nonmetallic-fabric interlayers.
The above-described hose as well features an adequate flexibility and is capable of withstanding the internal pressure. Moreover, it offers a higher durability as against that of the hose described in French Pat. No. 2,142,764, which is due to separation of individual reinforcing plies by the nonmetallic-fabric interlayers.
Due to a nonuniform distribution of the load from the internal pressure on the threads of each of the reinforcing plies, however, the application of this hose construction is limited to only relatively low internal pressures.
In addition, operation of this hose with a pulsating internal pressure gives rise to unbalanced inter-ply torque stemming from an unequal loading and an asymetrical wrapping of the threads forming the reinforcing plies, which results in a wear of the fabric interlayer due to rubbing and consequently in a failure of the construction.
Known in the art is still another hose disclosed in U.S. Pat. No. 3,212,528 and comprising an inner supporting tube and an outer protective cover, both of an elastic material, and reinforcing plies arranged between the supportion tube and the protective cover. Each of the reinforcing plies is a multiplicity or set of helically wrapped parallel threads (e.g., high-strength steel wires). The threads of successive plies are wrapped in opposite hands; the wrapping angle with respect to the geometric axis of the hose varies from the innermost reinforcing ply to the outermost one within the range of 51.degree. to 59.degree..
Wrapping of the threads at the angles within the above range derives from the fact that a wrapping angle close to 55.degree. provides for an equal loading of the threads from the internal pressure. A departure of the wrapping angles from this value is due to different diameters of wrapping for each of the reinforcing plies and depends on the amount of said reinforcing plies.
Each of the reinforcing plies is disposed between nonmetallic-fabric interlayers, the innermost of the interlayers being arranged directly on the supporting tube and serving for a uniform distribution of forces arising between the surface of the supporting tube and the reinforcing plies in operation.
The above-described hose offers an adequate flexibility, but is capable to withstand only an internal pressure. It may be used at a fairly high internal pressures, since the load from the internal pressure is uniformly distributed between all the reinforcing plies, and features a higher durability in operation of the hose under a pulsating internal pressure. The latter is accounted for by that the arising inter-layer torques are to a certain extent balanced due to an equal loading and a nearly symmetrical wrapping of the threads forming the reinforcing plies.
However, this hose is capable of withstanding the axial tension because wrapping of the threads which form the reinforcing plies at an angle of 51.degree. to 59.degree. to the geometrical axis of the hose fails to ensure stability of the hose cross-section under an axial tension, since it gives rise to considerable forces exerted by the threads upon the surface of the supporting tube. This upsets the equality of loading of the threads forming the reinforcing plies and consequently results in a failure of the construction.
In view of a considerable specific weight of this hose, it is apparent that it is incapable of operating even under the tension caused by its own gravity.
When this hose is used for operation under a pulsating internal pressure, there occur fairly high axial, radial, and volume deformations, which to certain extent impairs the operational durability of the hose.